how to use an arbitrary function in a wrapper function in Python

Question

I want to create a wrapper function something like the following:

def functionWrapper(function, **kwargs):
    """
        This function requires as input a function and a dictionary of named arguments for that function.
    """
    results=function(**kwargs)
        print results

def multiply(multiplicand1=0, multiplicand2=0):
    return multiplicand1*multiplicand2

def main():
    functionWrapper(
        multiply,
        {
            'multiplicand1': 3,
            'multiplicand2': 4,
        }
    )

if __name__ == "__main__":
    main()

I am running into difficulties with this implementation:

TypeError: functionWrapper() takes exactly 1 argument (2 given)

How should I address this problem? Is my use of the arbitrary function in the wrapper function function(**kwargs) reasonable? Thanks for your help.

EDIT: fixed error in specification of dictionary

Ashwini Chaudhary · Answer 1 · 2013-12-06T14:59:18.497

3

Use ** when passing the dict items to that function;

**{
   'multiplicand1': 3,
   'multiplicand2': 4,
  }

Output:

As pointed out by @svk in comments, functionWrapper's doctstring says:

This function requires as input a function and a dictionary of named arguments for that function.

So in that case you need to change the function definition to:

def functionWrapper(function, kwargs):

and also fix the typo in the dict otherwise you'll get 0 as answer:

'multiplicand1': 3,
'multiplicand1': 4,  #Change this to 'multiplicand2

'

edited Dec 06 '13 at 14:59

answered Dec 06 '13 at 14:54

Ashwini Chaudhary

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And note the change to `multiplicand2` for the 2nd multiplicand – doctorlove Dec 06 '13 at 14:56
This doesn't seem to be in line with the docstring for `functionWrapper`, which seems to say that `functionWrapper` should take two arguments: one callable and one dictionary, not a callable and an arbitrary number of keyword arguments. – svk Dec 06 '13 at 14:57

score 2 · Answer 2 · edited May 23 '17 at 12:07

2

Just change **kwargs to kwargs in function defenition:

def functionWrapper(function, kwargs):

What does ** (double star) and * (star) do for parameters?

edited May 23 '17 at 12:07

Community

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answered Dec 06 '13 at 14:53

ndpu

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score 1 · Answer 3 · answered Jun 11 '14 at 21:17

I feel like the spirit of this question is begging for this answer as well, to make it a more general wrapper.

def functionWrapper(func, *args, **kwargs):

    results = func(*args, **kw)

    print results 

def multiply(multiplicand1=0, multiplicand2=0):
    return multiplicand1*multiplicand2

if __name__ == "__main__":

    functionWrapper(multiply, multiplicand1=3, multiplicand2=4)
    # 12

    functionWrapper(multiply, 3, 4)
    # 12

    functionWrapper(multiply, 3)
    # 0

    functionWrapper(multiply)
    # 0

    functionWrapper(multiply, 5, multiplicand2=4)
    # 20

how to use an arbitrary function in a wrapper function in Python

3 Answers3